Hydrogen leak tests may be performed in fuel cell vehicles to determine anode integrity. Hydrogen may be used as a fuel source for fuel cells joined together to form a fuel cell stack. In the fuel cell stack, hydrogen is presented on the anode side whereas air is presented on the cathode side. The fuel cell stack generates electrical current in response to the electrochemical conversion of hydrogen and oxygen into water, which may then be used to drive various devices onboard the vehicle in addition to the vehicle itself.
Current approaches to anode leak detection include performing an anode leak test (ALT) while the vehicle is operated at low fuel cell power, for example, high-density traffic or as the vehicle is idled at a stoplight. Other approaches to detecting hydrogen leaks on the anode side of the fuel cell stack may be based on dropping vehicle power without supplementing power to the vehicle in order to perform the anode leak test. However, one problem with such leak tests based on identifying periods of low power is that infrequent checks may occur dependent on the type of operation a vehicle undergoes. For example, U.S. Pat. No. 8,524,405 discloses conducting an anode leak test during a vehicle shutdown process whereas U.S. Pat. No. 7,942,035 conducts a leak test in a fuel cell vehicle only when a zero-load requirement is satisfied. An alternate approach increases the frequency of anode leak tests by providing supplemental power to the vehicle while the anode leak test occurs. However, periods still exist in the drive cycle when anode leak tests may not be performed (e.g., under high-load driving and/or low battery state-of-charge, etc.). When configured with a power source to provide supplementary power, fuel cell vehicles may include additional equipment such as an electric motor that increases a vehicle cost.
The inventors herein have recognized the above issues and disclose methods for identifying an anode leak during vehicle operation. In one described embodiment, an anode leak test is performed while the vehicle is operated with a load by comparing a current generated by the fuel cell to a current predicted for a flow of hydrogen to the fuel cell, the flow of hydrogen to the fuel cell maintaining a vehicle power during the anode leak test. When configured with this arrangement, the method further allows for reducing the vehicle power responsive to identifying the anode leak while still providing sufficient power to operate the vehicle via the hydrogen flow. As described, adjusting the vehicle power occurs responsive to the actuation of a tank valve associated with a fuel storage tank that is included to store hydrogen fuel on-board the vehicle. Closing of the tank valve may lead to a reduction of the hydrogen fuel flow that reduces the vehicle power during operation. The advantage of the method disclosed is that the anode leak test may be performed during vehicle operation, for example, as the vehicle is being operated and driven along a roadway. Another advantage of the disclosed methods is that checks for anode leaks may be performed at a higher frequency during operation for a substantially real-time determination of the degradation status of the fuel system. In this way, the technical result is achieved that conductance of the anode leak test may be extended to occur during more vehicle operating conditions for more frequent checking of anode leaks during vehicle operation, for example, while the vehicle is driven on the road.
In one example, the method may comprise a statistical comparison including a two-sample student test that accounts for an average current and envelope thereof to determine an extent of difference between the current generated by the hydrogen fuel cell and the current predicted for the flow of hydrogen into the fuel cell. The advantage of a statistical comparison based on current and/or power generated therefrom during operation is that an estimate on the size of the leak may be made based on the extent of the difference identified. Thus, in some embodiments, the method further comprises determining a size of the leak during operation responsive to identifying the anode leak while maintaining the vehicle power based on the flow of hydrogen to the fuel cell. The advantage of including such methods is the inclusion of alternate modes of vehicle operation in the presence of an anode leak. For simplicity, the system herein is described in terms of the hydrogen fuel cell, although the methods described may also be included within hybrid vehicles configured to provide supplementary power while the hydrogen fuel cell is shut off.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.